I'm running an O.S. .46AX stock muffler about a gallon through it and it does not transition nicely from idle to full throttle, (its on an ex-treme 330 profile, 3D type flight) and I need better throttle transition. The high-end needle is still set a little rich, but I'm not sure if this is an idle adjustment screw problem or what, I haven't had to mess with these in the past on my other O.S. engines. Thanks for any response

If it is stumbling a little as it accelerates, the idle is too rich. OS tends to send their engines out just a tad rich on the idle (safer than lean). Peak out the high end to just a few clicks richer than peak. Just lean the idle out in 1/8 turn increments until the transition is smooth. Then retune the high end if needed and enjoy.

Inside the throttle arm you will see a straight slot screw. Turn it clock wise 1/8 to 1/4 (at the most) turns at a time. Shut the motor off the make the adjustement and open the throttle all the way when you do.

Restart and test. I've had a couple students lately needing over 1/2 turn just to get it to idle without snuffing the fire out.

Just tweak and test, its a fairly sensitive adjustment.

Yup, got a small flat-head screwdriver? Sounds like your problem may be easy to fix! I have never had an engine (new or used) that did NOT need the idle mixture adjusted.... I like to start also 1/8th of a turn at a time- I start it tune for full thr. quickly then go to idle, let it idle for 30 seconds (or as long as it will idle reasonably) then advance the throttle QUICKLY- if it sputters it is rich and you need to go another 1/8th lean (clockwise) if it just dies purty quick it was too lean- (probably not the case with yours-)

Start it up again and repeat- Keep doing that until your transition is as fast as you move the stick!

Keep us posted!

Thanks guys, this is what I thought it was, will probably get the chance to try it here today, although the weather is kinda ugly right now.

That's why we have garages here.